Heterogenous expression of Ca2+-dependent K+ currents by Müller glial cells.
The flavoid phloretin was used to study large-conductance, Ca2+-activated K+ (BKCa) channel-mediated currents in isolated porcine Müller (retinal glial) cells. In excised membrane patches, application of phloretin (100 microM) increased the open probability of single BKCa channels. In whole-cell records, phloretin increased the amplitude of an outward current which was blockable by iberiotoxin (40 nM) and TEA (1 mM), and, thus, was identified as a BKCa current. Only 50% of the investigated cells expressed phloretin-sensitive BKCa currents. Cells with phloretin-sensitive BKCa currents responded to glutamate (500 microM) with an increase of the amplitude of this current, whereas glutamate had no effects on the K+ currents of cells without BKCa currents. As glutamate is a major neurotransmitter of the retina, and the membrane properties of Müller cells are largely determined by their K+ channels, the observed data may shed new light onto the functions of retinal glia.
Bringmann
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Paul Flechsig Institute of Brain Research, Department of Neurophysiology, University of Leipzig, Germany.
Reichenbach
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D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D018698:Glutamic Acid / Q000494:pharmacology; D009457:Neuroglia / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D010693:Phloretin / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D013552:Swine; D014118:Toxins, Biological / Q000494:pharmacology
D015220:Calcium Channels; D010455:Peptides; D015221:Potassium Channels; D014118:Toxins, Biological; D018698:Glutamic Acid; C064719:iberiotoxin; D010693:Phloretin